System and method for detecting victim signal in MB-OFDM UWB communication system

ABSTRACT

To detect a victim signal in an ultra wideband communication system, fast Fourier transform of a received signal including a plurality of time symbols is performed to generate a signal including a plurality of frequency symbols, it is determined whether a first signal is present in a first region of the signal, and if a first signal is present, the first signal is detected as a first victim signal. Next, an error signal is generated based on the signal including the plurality of frequency symbols, it is determined whether a second signal is present in a second region of the error signal, and if a second signal is present, the second signal is detected as a second victim signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2010-0088123 filed in the Korean IntellectualProperty Office on Sep. 8, 2010, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method for detecting a victim signalin a multi-band orthogonal frequency division multiplexing ultrawideband communication system.

(b) Description of the Related Art

For the use of UWB (Ultra Wide Band) systems in a particular frequencyband to protect communication systems that exist or will be introducedin the future, a technology standard regulates that other communicationsignal of a certain level is to be detected and measures are to be takento protect the detected communication signal. There are no specificworldwide common standards on the type of victim signal, a victimdetection level, etc. to apply such a DAA (Detect And Avoid) technologystandard to an actual communication system. Also, a victim communicationsystem to be protected, a victim detection level for applying the avoidtechnology to UWB, and so on are differently set according to differentcountries.

The detect and avoid technology standard, as discussed so far, is mainlyabout an avoid algorithm that sets a victim signal detection level forprotecting a victim signal and is applicable according to the victimsignal detection level. For example, there is an avoid algorithm that,if a packet error rate received by MAC (Medium Access Control) is higherthan a reference value, discriminates whether the packet error ratecomes from other UWB device or other communication equipment and thenperforms an interference avoiding operation.

Moreover, to prevent UWB signal interference in a WiMax band for avictim signal, an avoid algorithm is proposed which controls a bandincluding a null tone among 128 IFFT-mapped tones of an ultra widebandsignal to be shifted to a band where an interference with an WiMaxsignal occurs. In addition, there is an avoid algorithm in which a UWBdevice detects the strength of a received signal of a UWB communicationband, and if the detected strength of the received signal is within adetermined range of interference, determines that it has a possibilityof interference with other devices and selects a different UWBcommunication frequency band.

To apply the detect and avoid technology standard, when a victim signalof a specific received signal level is detected from a UWB device, it isnecessary for the UWB device to decrease its communication output orswitch its communication band to another frequency band within aspecific length of time. Typically, in order to detect such a victimsignal of a specific level, the presence or absence of a victim signalof a specific level is detected, while the communication of the UWBdevice is being stopped, within a specific time range of avoidancedefined by the detect and avoid technology standard. In this case, thecommunication of the UWB device has to be stopped to detect a victimsignal at specific time intervals even when no victim signal is present,thus significantly lowering the throughput of the UWB communicationdevice.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a method fordetecting a victim signal during communication in an MB-OFDM UWB system,which can meet the detect and avoid technology standard.

An exemplary embodiment of the present invention provides a system fordetecting a victim signal in an ultra wideband communication system, thesystem including:

a fast Fourier transform unit that performs fast Fourier transform of areceived signal including a plurality of time symbols to output a signalincluding a plurality of frequency symbols; a DFL (Detection AlgorithmFor Low Signal Noise Ratio) processor that checks and detects thepresence or absence of a victim signal in a first signal correspondingto a first region of the input fast-Fourier-transformed signal; amonitor that monitors an error signal generated based on a signalobtained by performing channel compensation on thefast-Fourier-transformed signal and a signal obtained by performingsymbol determination on the channel-compensated signal; and a DFH(Detection Algorithm For High Signal Noise Ratio) processor that checksand detects the presence of a victim signal in a second signalcorresponding to a second region of the error signal.

An exemplary embodiment of the present invention provides a method ordetecting a victim signal in an ultra wideband communication system, themethod including:

performing fast Fourier transform of a received signal including aplurality of time symbols to generate a signal including a plurality offrequency symbols; determining the presence or absence of a first signalin a first region of the signal including the plurality of frequencysymbols, and, if a first signal is present, detecting the first signalas a first victim signal; generating an error signal based on the signalincluding the plurality of frequency symbols; and receiving the errorsignal, determining the presence or absence of a second signal in asecond region of the error signal, and, if a second signal is present,detecting the second signal as a second victim signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing UWB frequency allocation to which ageneral detect and avoid technology standard is applied.

FIG. 2 is an illustration showing a victim signal detection environmentusing a general UWB reception SNR.

FIG. 3 is a structural diagram of a system for detecting a victim signalaccording to SNRs according to an exemplary embodiment of the presentinvention.

FIG. 4 is an illustration showing a structure of a system for detectinga victim signal in a first region according to an exemplary embodimentof the present invention.

FIG. 5 is an illustration showing a simulation result of DFL applicationaccording to a first exemplary embodiment of the present invention.

FIG. 6 is an illustration showing a simulation result of DFL applicationaccording to a second exemplary embodiment of the present invention.

FIG. 7 is an illustration showing a victim signal detection algorithmaccording to the second exemplary embodiment of the present invention.

FIG. 8 is an illustration showing a simulation result of DHF applicationaccording to the second exemplary embodiment of the present invention.

FIG. 9 is an illustration showing the performance of the victim signaldetection algorithm according to an exemplary embodiment of the presentinvention.

FIG. 10A and FIG. 10B are flowcharts showing a method for detecting avictim signal according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, only certain exemplaryembodiments of the present invention have been shown and described,simply by way of illustration. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentinvention. Accordingly, the drawings and description are to be regardedas illustrative in nature and not restrictive. Like reference numeralsdesignate like elements throughout the specification.

Throughout the specification, unless explicitly described to thecontrary, the word “comprise” and variations such as “comprises” or“comprising”, will be understood to imply the inclusion of statedelements but not the exclusion of any other elements.

Hereinafter, a method for detecting a victim signal according to anexemplary embodiment of the present invention will be described withreference to the drawings.

FIG. 1 is an illustration showing UWB frequency allocation to which ageneral detect and avoid technology standard is applied.

As shown in FIG. 1, the DAA (Detect And Avoid) technology standardrequires that, if other wireless base station signal of a frequency bandhigher than a predetermined frequency band (e.g., −80 dBm/MHz) is sensedduring the operation of a UWB (Ultra Wide Band) system, the frequencyband is reduced to a predetermined frequency band (e.g., −70 dBm/MHz) orlower or switch to another frequency band. Examples of wirelesstechnologies currently offering the possibility of adopt the detect andavoid technology standard in the 3100 to 4800 MHz frequency band include4 G communication, Wibro, and WiMax.

Generally, in order to detect a victim signal of a specific leveldefined by the detect and avoid technology standard, the presence orabsence of a victim signal of a specific level is detected, while thecommunication of the UWB device is being stopped, within a specific timerange of avoidance. In this case, the communication of the UWB devicehas to be stopped to detect a victim signal at specific time intervaleven when no victim signal is present, and thus the throughput of theUWB communication device is lowered.

Accordingly, in the exemplary embodiment of the present invention,rather than stopping UWB communication at specific time intervals ofavoidance and detecting a victim signal, the UWB communication isstopped only when a victim signal is sensed as being present during theUWB communication, and an algorithm for detecting a victim signal higherthan a specific level is executed detect a victim signal. Prior todescribing a victim signal detection environment for applying thisalgorithm, a general victim signal detection environment will bedescribed with reference to FIG. 2.

FIG. 2 is an illustration showing a victim signal detection environmentusing a general UWB reception SNR (signal to noise ratio). In FIG. 2,underlined numbers represent SNR and squared numbers represent loss.

As shown in FIG. 2, a communication environment of a UWB system may bedivided into a low SNR region (hereinafter, referred to as a firstregion for convenience of description) in which the power density of avictim signal is higher than the power density of a UWB signal and ahigh SNR region (hereinafter, referred to as a second region forconvenience of description) in which the power density of a victimsignal is similar to or lower than the power density of a UWB signal.

The detection level of a victim signal is estimated to be higher than aUWB reception power in the first region located at a long distance froma transmitting end of the UWB system. Thus, the presence or absence of avictim signal can be easily determined by detecting a frequency domainsignal of a received signal. On the contrary, although the SNR is highfor a near distance from the transmitting end of the UWB system, thedetection level of a victim signal lies below a UWB reception signallevel. Thus, it is difficult to determine the presence or absence of avictim signal by a simple frequency domain estimation algorithm.

When considering an actual UWB system operation environment and thepossibility of the presence of a victim signal, an algorithm fordetecting a victim signal in various SNR environments is needed.Preferably, such a victim signal detection algorithm is designed to bedivided into an algorithm that works in low SNR and an algorithm thatworks in high SNR according to SNRs. This will be described withreference to the system structure of FIG. 3.

FIG. 3 is a structural diagram of a system for detecting a victim signalaccording to SNRs according to an exemplary embodiment of the presentinvention.

As shown in FIG. 3, a victim signal detection system 100 comprises a FFT(Fast Fourier Transform) unit 110, a DFL (Detection Algorithm For LowSignal Noise Ratio) processor 120, a channel estimator 130, a channelcompensator 140, a symbol determiner 150, an adder 160, a monitor 170,and DFH (Detection Algorithm For High Signal Noise Ratio) processor 180.

The FFT unit 110 FFT-transforms an input received signal to convert asignal on a time axis into a signal on a frequency axis.

The DFL processor 120 receives a signal output from the FFT unit 110,and checks whether a victim signal is present in the received signal.Among the signals output from the FFT unit 110, only the signals(hereinafter, referred to as first signals) having a power densityhigher than a UWB signal power density, corresponding to the firstregion, are processed. In case any victim signal is present, the UWBsystem is stopped and a procedure subsequent to the stopping isperformed. The DFL processor 120 will be described in detail later.

The channel estimator 130 estimates a channel gain by receiving a signalon a frequency axis output from the FFT unit 110 and a stored referencesignal (Reference CE) and conjugating the two signals and accumulatingthe resulting values. The estimated channel gain is output as a channelfrequency response HLS. A method of estimating a channel gain is alreadyknown, so a detailed description thereof will be omitted in theexemplary embodiment of the present invention.

The channel compensator 140 receives the channel frequency responseoutput from the channel estimator 130 and the signal output from the FFTunit 110 and outputs a channel-compensated signal. In channelcompensation, both the phase and amplitude of a signal are to becompensated by the following Equation 1. Although the exemplaryembodiment of the present invention will be described taking an examplein which the channel compensator 140 outputs 6 channel compensationsymbols, the present invention is not necessarily limited thereto.Ŷ=Y/Ĥ _(LS)  (Equation 1)

Where Ŷ is the output of the channel estimator 130, Y is the outputsignal of the FFT unit 110, Ĥ_(LS) is the channel frequency responseobtained from the 6 channel compensation OFDM symbols.

The symbol determiner 150 receives the channel-compensation signal fromthe channel compensator 140, and determines a symbol and outputs it.

The adder 160 receives the channel-compensated signal from the channelcompensator 140 and the symbol output from the symbol determiner 150,and outputs a difference value between them. That is, to detect a victimsignal, the adder 160 calculates an error value between the value beforesymbol determination and the value after symbol determination andoutputs an error signal (e(n)).

The monitor 170 maps the error signal output from the adder 160 to 128FFT subcarrier locations in order for the DFH processor 180 to checkwhether a victim signal is present.

The DFH processor 180 checks whether a victim signal is present in thesignal based on the signal output from the monitor 170. That is, tooperate a DFH algorithm in the second region, the presence of a victimsignal is checked by detecting signals (hereinafter, referred to assecond signals) having a power density similar to or lower than the UWBsignal power density. In case any victim signal is present, the UWBsystem is stopped and a procedure subsequent to the stopping isperformed. The DFH processor 180 will be described in detail later.

The DFL processor 120 employing a victim signal detection algorithm forlow SNR in the thus-configured victim signal detection system 100 willbe described with reference to FIG. 4.

FIG. 4 is a structural diagram of the DFL processor, according to anexemplary embodiment of the present invention.

As shown in FIG. 4, the DFL processor 120 according to the exemplaryembodiment of the present invention which receives signals outputthrough the FFT unit 110 and tracks the position of a subcarrier with avictim signal among a plurality of subcarriers based on a plurality ofselected time symbols comprises a first operation unit 121, a secondoperation unit 122, a third operation unit 123, and a location detectionunit 124.

The FFT unit 110 operating in conjunction with the DFL processor 120comprises a data aligning unit 111 and a plurality of Fourier transformunits 112. Although the exemplary embodiment of the present inventionwill be described with respect to the FFT unit 100 comprising a dataaligning unit 111 and a plurality of Fourier transform units 112 forconvenience of description, the present invention is not necessarilylimited thereto.

The FFT unit 110 will be described first for convenience of description.The data aligning unit 111 selects a predetermined number of timesymbols among a plurality of time symbols included in a digitaldetection signal, and outputs a plurality of selected time symbols inparallel.

The plurality of Fourier transform units 112 respectively correspond tothe plurality of selected time symbols, and output a plurality offrequency symbols respectively corresponding to the plurality ofselected time symbols by performing Fourier transform on each of theplurality of selected time symbols. Each of the plurality of frequencysymbol comprises a plurality of frequency samples that respectivelycorrespond to the plurality of subcarriers.

The first operation unit 121 of the DFL processor 120 adds the pluralityof frequency samples corresponding to each subcarrier and outputs aplurality of, sample sums respectively corresponding to each of theplurality of subcarriers. Each of the plurality of sample sumscorresponds to a complex number value.

The second operation unit 122 adds the absolute values of the real andimaginary parts of each sample sum based on the plurality of samplesums, and outputs a plurality of sample absolute values thatrespectively correspond to the plurality of sample sums.

The third operation unit 123 divides the sum of the plurality of sampleabsolute values by a value corresponding to a subcarrier detection rangebased on the plurality of sample absolute values to output a referencevalue for determining the presence or absence of a victim signal foreach of the plurality of subcarriers.

The location detection unit 124 compares each of the plurality of sampleabsolute values with the reference value to detect a subcarrier where avictim signal is located. That is, if a sample absolute value is greaterthan the reference value, this indicates that a victim signal is locatedat the corresponding position, a subcarrier corresponding to the sampleabsolute value is detected and output.

In other words, first of all, an n number of 128 FFTs is performed usingan MB-OFDM UWB reception structure in order to detect a subcarrier witha victim signal among 128 FFT subcarriers of an MB-OFDM UWB system.Then, the sum of the subcarriers that have performed the FFTs isobtained.

Using the sum of the 128 FFT results, the sum Z_(k) (k=0, 2, . . . ,127) of the absolute values of the real and imaginary parts of each ofthe subcarriers is obtained. Then, a reference value Z_(ref) to be usedas a reference for determining the presence or absence of a victimsignal is calculated for each subcarrier by the following Equation 2:

$\begin{matrix}{Z_{ref} = {\left( {\sum\limits_{k = 0}^{127}Z_{k}} \right)/n}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

where n indicates a random number between 1 and 128.

After calculating the reference value used as the reference, the sumZ_(k) of the absolute values obtained previously are the reference valueare compared with each other for each of the 128 subcarriers to selectthe location of a victim signal. An example of selecting the location ofa victim signal will be described with reference to FIG. 5.

FIG. 5 is an illustration showing a simulation result of DFL applicationaccording to a first exemplary embodiment of the present invention.

(a) of FIG. 5 is an illustration showing a signal in a low SNRenvironment among the signals passed through the FFT 110. As illustratedin (a) of FIG. 5, in a low SNR region where the power density of avictim signal is higher than the power density of a UWB signal, thelocation of the victim signal can be detected by applying DFL. Thesignal after the application of DFL is as shown in (b) of FIG. 5. Thatis, as illustrated in (b) of FIG. 5, the location of a subcarriergreater than the reference value is selected as the location of a victimsignal.

FIG. 6 is an illustration showing a simulation result of DFL applicationaccording to a second exemplary embodiment of the present invention.

As illustrated in (a) of FIG. 6, under high SNR conditions, the PSD(Power Spectral Density) of a victim signal is too low, as compared tothat of a UWB reception signal, so the victim signal does not appear onthe spectrum, being covered by the UWB reception signal. In the casewhere the victim signal received in a high SNR environment is not seen,being covered by the UWB signal, if the victim signal detectionalgorithm DFL available at low SNR, as designed in FIG. 4, is adopted todetect a victim signal, no victim signal is detected as shown in (b) ofFIG. 6.

Therefore, the DFH processor for detecting a victim signal in a high SNRenvironment will be described with reference to FIG. 7.

FIG. 7 is an illustration showing a structure of the DFH processoraccording to an exemplary embodiment of the present invention.

As shown in FIG. 7, the DFH processor 180 according to the exemplaryembodiment of the present invention receives signals output from themonitor 170 and tracks the location of a subcarrier with a victimsignal, and comprises a fourth operation unit 181, a fifth operationunit 182, a sixth operation unit 183, and a location detection unit 184.

The fourth operation unit 181 receives an error signal (e(n)) outputfrom the monitor 170 of FIG. 3, and adds a plurality of frequencysamples respectively corresponding to the plurality of subcarriers in anOFDM symbol, and outputs a plurality of sample sums respectivelycorresponding to the plurality of subcarriers. Each of the plurality ofsample sums corresponds to a complex number value.

The fifth operation unit 182 adds the absolute values of the real andImaginary parts of each sample sum based on the plurality of samplesums, and outputs a plurality of sample absolute values thatrespectively correspond to the plurality of sample sums.

The sixth operation unit 183 divides the sum of the plurality of sampleabsolute values by a value corresponding to a subcarrier detection rangebased on the plurality of sample absolute values to output a referencevalue for determining the presence or absence of a victim signal foreach of the plurality of subcarriers.

The location detection unit 184 compares each of the plurality of sampleabsolute values with the reference value to detect a subcarrier where avictim signal is located.

That is, to detect a victim signal in a high SNR environment, thepresence or absence of a victim signal is determined using a valueobtained by subtracting the final determined d(n) from the signal d(n)whose l-th received symbol is channel-compensated as in Equation 3:Y _(l,k) =d(n)−d(n)  (Equation 3)

where l denotes the l-th symbol, and k denotes the k-th subcarrier.

The sum of the subcarriers is obtained by using the 128 subcarriervalues in the OFDM symbol obtained in Equation 3. Using the sum of the128 FFT results, the sum Z_(k) (k=0, 2, . . . , 127) of the absolutevalues of the real and imaginary parts of each of the subcarriers isobtained. Then, a reference value Z_(ref) to be used as a reference fordetermining the presence or absence of a victim signal for eachsubcarrier is calculated by the following Equation 4:

$\begin{matrix}{Z_{ref} = {\left( {\sum\limits_{k = 0}^{127}Z_{k}} \right)/n}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

where n indicates a random number between 1 and 128.

After calculating the reference value used as the reference, the sumZ_(k) of the absolute values obtained previously are the reference valueare compared with each other for each of the 128 subcarriers to selectthe location of a victim signal. The thus-selected location of a victimsignal will be described with reference to FIG. 8.

FIG. 8 is an illustration showing a simulation result of DHF applicationaccording to the second exemplary embodiment of the present invention.

As shown in (a) of FIG. 8, the PSD (Power Spectral Density) of a victimsignal is too low, as compared to that of a UWB reception signal, so thevictim signal does not appear on the spectrum, being covered by the UWBreception signal. Accordingly, using the algorithm structure of FIG. 7,the location of a victim signal covered by a UWB signal can be detectedas show in (b) of FIG. 8. That is, although it is difficult to detect avictim signal from UWB signals including a victim signal merely byperforming FFT in the way DFL is performed, if the victim signaldetection algorithm according to the exemplary embodiment of the presentinvention is used, the location of a victim signal can be accuratelydetected as shown in (b) of FIG. 8.

Next, to exhibit the performance of the victim signal detectionalgorithm during UWB communication, the performances of DFL and DFHunder an SNR environment of −6 dB to 48 dB will be described withreference to FIG. 9.

FIG. 9 is an illustration showing the performance of the victim signaldetection algorithm according to an exemplary embodiment of the presentinvention.

It is assumed that the channel environment is set to an AWGN (AdditiveWhite Gaussian Noise) condition, and a victim signal is received at −70dBm in a 10 MHz bandwidth. A number (e.g., DFL_(—)9) of FIG. 9represents the number of packets used for performance evaluation, and 12PLCP (Packet Layer Convergence Procedure) header OFDM symbols are usedto evaluate the performance of the victim signal detection algorithmregardless of the data transmission rate of UWB communication.

As shown in FIG. 9, as the detection ranges of DFL and DFH overlapwidely, it can be found out that a victim signal can be detected overthe entire SNR range during UWB communication by using both of the twoalgorithms.

Next, a method for detecting a victim signal by the victim signaldetection system 100 will be described with reference to FIGS. 10A and10B.

FIG. 10A and FIG. 10B are flowcharts showing a method for detecting avictim signal according to an exemplary embodiment of the presentinvention.

FIG. 10A is a flowchart showing a method for detecting a victim signalby the DFL processor 120, and FIG. 10B is a flowchart showing a methodfor detecting a victim signal by the DFH processor 180. The DFLprocessor 120 and the DFH processor 180 operate independently, ratherthan operating in conjunction with each other, such that upon detectinga victim signal by any one of the processors, the operation of the UWBsystem is stopped to proceed to the subsequent procedure. In theexemplary embodiment of the present invention, the description of theprocedure subsequent to the detection of a victim signal will beomitted.

First, as illustrated in FIG. 10A, a plurality of Fourier transformunits 112 of the FFT unit 110 perform Fourier transform of a receivedsignal and output the signal. Each of a plurality of frequency symbolsoutput at this time comprises a plurality of frequency samplesrespectively corresponding to the plurality of subcarriers.

The first operation unit 121 receives subcarriers serving as a pluralityof signals output from the FFT unit 110 (S100), and adds the pluralityof frequency samples respectively corresponding to each subcarrier basedon each of the plurality of frequency symbols, and obtains a pluralityof sample sums (S110). A sample value is a complex number valueconsisting of real and imaginary parts. Accordingly, the plurality ofsample sums obtained in the step S110 are calculated as a plurality ofsample absolute values obtained by adding the absolute values of realand imaginary parts by the second operation unit 122 (S120).

The third operation unit 123 outputs a reference value for determiningthe presence or absence of a victim signal based on the plurality ofsubcarriers (S130). Then, the location detection unit 124 compares eachof the plurality of sample absolute values calculated in the step S120with the reference value output in the step S130 (S140), and detects asubcarrier where a victim signal is located as well as the presence orabsence of a victim signal (S150).

That is, if a sample absolute value is greater than the reference value,this indicates that a victim signal is present in the correspondingsample, a subcarrier corresponding to the sample is detected. However,if the sample absolute value is less than the reference value, thisindicates that no victim signal is present in the corresponding sample,and hence the procedure is performed again starting from the step S100.

When a subcarrier where a victim signal is located is detected, anavoidance operation for protecting the victim signal is (S160). As theavoidance operation is already known, the detailed description thereofwill be omitted in the exemplary embodiment of the present invention.The thus-detected subcarrier is in the location of a victim signalpresent within a first signal having a higher power density than thepower density of a UWB signal.

On the other hand, when a victim signal is present within a secondsignal having a power density similar to or lower than the power densityof the UWB signal, the victim signal is detected in the same procedureas shown in FIG. 10B.

That is, the fourth operation unit 181 receives an error signal outputfrom the monitor 170 (S200). The error signal (e(n)) is an error valuebetween the values before and after symbol determination by the adder160.

The plurality of frequency samples 128 respectively corresponding toeach subcarrier are added together based on each of the plurality offrequency symbols aligned in units of 128 subcarriers to obtain aplurality of sample sums (S210). A sample value is a complex numbervalue consisting of real and imaginary parts. The plurality of samplesums obtained in the step S210 are calculated as a plurality of sampleabsolute values obtained by adding the absolute values of real andimaginary parts by the fifth operation unit 182 (S220).

The sixth operation unit 183 outputs a reference value for determiningthe presence or absence of a victim signal based on the plurality ofsubcarriers (S230). Then, the location detection unit 184 compares eachof the plurality of sample absolute values calculated in the step S220with the reference value output in the step S230 (S240), and detects asubcarrier where a victim signal is located, as well as the presence orabsence of a victim signal (S250).

That is, if a sample absolute value is greater than the reference value,this indicates that a victim signal is present in the correspondingsample, a subcarrier corresponding to the sample is detected. However,if the sample absolute value is less than the reference value, thisindicates that no victim signal is present in the corresponding sample,and hence the procedure is performed again starting from the step S200.

When a subcarrier where a victim signal is located is detected, anavoidance operation for protecting the victim signal is (S260). As theavoidance operation is already known, the detailed description thereofwill be omitted in the exemplary embodiment of the present invention.

According to an exemplary embodiment of the present invention,throughput can be guaranteed in the case of absence of a victim signalby stopping UWB communication and performing a victim signal detectionalgorithm only when a UWB device has detected the presence of a victimsignal during UWB communication.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A system for detecting a victim signal in anultra wideband communication system, the system comprising: a fastFourier transform unit that performs fast Fourier transform of areceived signal including a plurality of time symbols to output a signalincluding a plurality of frequency symbols; a DFL (Detection AlgorithmFor Low Signal Noise Ratio) processor that checks and detects thepresence of a victim signal in a first signal corresponding to a firstregion of the input fast-Fourier-transformed signal; a monitor thatmonitors an error signal generated based on a signal obtained byperforming channel compensation on the fast-Fourier-transformed signaland a signal obtained by performing symbol determination on thechannel-compensated signal; and a DFH(Detection Algorithm For HighSignal Noise Ratio) processor that checks and detects the presence of avictim signal in a second signal corresponding to a second region of theerror signal.
 2. The system of claim 1, wherein each of the plurality offrequency symbols comprises a plurality of frequency samplesrespectively corresponding to a plurality of subcarriers, and the DFLprocessor comprises: a first operation unit that adds the plurality offrequency samples respectively corresponding to each subcarrier based oneach of the plurality of frequency symbols, and outputs a plurality ofsample sums respectively corresponding to the plurality of subcarriers;a second operation unit that adds the absolute values of the real andimaginary parts of each sample sum based on the plurality of samplesums, and outputs a plurality of sample absolute values thatrespectively correspond to the plurality of sample sums; a thirdoperation unit that divides the sum of the plurality of sample absolutevalues by a predetermined subcarrier detection range value based on theplurality of sample absolute values to output a reference value; alocation detection unit that compares each of the plurality of sampleabsolute values with the reference value to generate information onwhere a victim signal is located.
 3. The system of claim 2, wherein thefirst region is a region in which the power density of a victim signalis higher than the power density of a received signal, and the firstsignal has a higher power density than the received signal power densityin the first region.
 4. The system of claim 1, wherein the error signalcomprises a plurality of frequency samples respectively corresponding toa plurality of subcarriers, and the DFH processor comprises: a fourthoperation unit that adds the plurality of frequency samples respectivelycorresponding to each subcarrier based on each of the plurality offrequency symbols, and outputs a plurality of sample sums respectivelycorresponding to the plurality of subcarriers; a fifth operation unitthat adds the absolute values of the real and imaginary parts of eachsample sum based on the plurality of sample sums, and outputs aplurality of sample absolute values that respectively correspond to theplurality of sample sums; a sixth operation unit that divides the sum ofthe plurality of sample absolute values by a predetermined subcarrierdetection range value based on the plurality of sample absolute valuesto output a reference value; and a location detection unit that compareseach of the plurality of sample absolute values with the reference valueto generate information on where a victim signal is located.
 5. Thesystem of claim 4, wherein the second region is a region in which thepower density of a victim signal is similar to or lower than the powerdensity of a received signal, and the second signal has a power densitysimilar to or lower than the received signal power density in the secondregion.
 6. The system of claim 1, comprising: a channel estimator thatestimates a channel gain by receiving a signal output from the FFT unitand a stored reference signal and conjugating the output signal and thereference signal and accumulating the resulting values, and outputs achannel frequency response; and a channel compensator that receives thechannel frequency response output from the channel estimator and thesignal output from the FFT unit and outputs a channel-compensatedsignal.
 7. The system of claim 6, wherein the channel compensatorcompensates for both the phase and amplitude of a signal.
 8. The systemof claim 6, further comprising: a symbol determiner that receives thechannel-compensation signal from the channel compensator and determinesa symbol; an adder that receives the channel-compensated signal from thechannel compensator and the symbol output from the symbol determiner,and outputs a difference value between the signal and the symbol as anerror signal.
 9. A method for detecting a victim signal in an ultrawideband communication system, performing fast Fourier transform (FFT)of a received signal including a plurality of time symbols to generate asignal including a plurality of frequency symbols; determining thepresence or absence of a first signal in a first region of the signalincluding the plurality of frequency symbols, and, if a first signal ispresent, detecting the first signal as a first victim signal; generatingan error signal based on the signal, wherein the generated error signalis obtained by performing channel compensation on both the FFT of thereceived signal and another signal obtained by performing symboldetermination on the channel compensated signal, including the pluralityof frequency symbols; and receiving the error signal, determining thepresence or absence of a second signal in a second region of the errorsignal, and, if a second signal is present, detecting the second signalas a second victim signal.
 10. The method of claim 9, wherein each ofthe plurality of frequency symbols comprises a plurality of frequencysamples respectively corresponding to a plurality of subcarriers, andthe detecting of the first victim signal comprises: adding the pluralityof frequency samples respectively corresponding to each subcarrier basedon each of the plurality of frequency symbols, and outputting aplurality of sample sums respectively corresponding to the plurality ofsubcarriers; adding the absolute values of the real and imaginary partsof each sample sum based on the plurality of sample sums, and outputtinga plurality of sample absolute values that respectively correspond tothe plurality of sample sums; dividing the sum of the plurality ofsample absolute values by a predetermined subcarrier detection rangevalue based on the plurality of sample absolute values to output areference value; and comparing each of the plurality of sample absolutevalues with the reference value to generate the location information ofthe first victim signal.
 11. The method of claim 9, wherein the errorsignal comprises a plurality of frequency samples respectivelycorresponding to a plurality of subcarriers, and the detecting of thesecond victim signal, wherein the second victim signal is responsive tothe generated error signal and comprises: adding the plurality offrequency samples respectively corresponding to each subcarrier based oneach of the plurality of frequency symbols, and outputting a pluralityof sample sums respectively corresponding to the plurality ofsubcarriers; adding the absolute values of the real and imaginary partsof each sample sum based on the plurality of sample sums, and outputtinga plurality of sample absolute values that respectively correspond tothe plurality of sample sums; dividing the sum of the plurality ofsample absolute values by a predetermined subcarrier detection rangevalue based on the plurality of sample absolute values to output areference value; and comparing each of the plurality of sample absolutevalues with the reference value to generate the location information ofthe second victim signal.
 12. The method of claim 10, furthercomprising, after the generating of the location information, performingan avoidance operation for protecting the first victim signal or thesecond victim signal.
 13. The method of claim 11, further comprising,after the generating of the location information, performing anavoidance operation for protecting the first victim signal or the secondvictim signal.
 14. The method of claim 9, wherein the generating of theerror signal comprises: estimating a channel gain by receiving a signaloutput from the FFT unit and a stored reference signal and conjugatingthe output signal and the reference signal and accumulating theresulting values, and outputting a channel frequency response; andoutputting a channel-compensated signal based on the channel frequencyresponse and the fast-Fourier-transformed signal; receiving thechannel-compensated signal and determining a symbol; and receiving thechannel-compensated signal and the symbol output from the symboldeterminer, and outputting a difference value between the signal and thesymbol as an error signal.
 15. The method of claim 14, wherein, in theoutputting of the channel-compensated signal, thefast-Fourier-transformed signal is divided by the channel frequencyresponse to output the channel-compensated signal.